Although units may be commanded by clicking on the map, the four unit buttons can be convenient as well. 

The first button disbands a civilian and sends the worker back to industry. This is useful if you have nothing more for the civilian to do. For military units this button brings up the details of a group of regiments. 

Other unit buttons include: the later button (an arrow), which continues to the next unit in the cycle; the done button (an X), which ends the turn for the selected unit; and the sleep button, which removes the selected unit from the cycle next turn.